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Патент USA US3091746

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May 28, 1963
Filed March 5, 1957
9 Sheets-Sheet 1
Ma)’ 28, 1963
Filed March 5, 1957
9 Sheets-Sheet 2
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May 28, 1963
Filed March 5, 1957
9 Sheets-Sheet 3
May 28, 1963
Filed March 5, 1957
9 Sheets-Sheet 4
"017 I00
/A:9MNUM SLEEVE \IX \/ / /
May 28, 1963
Filed March 5, 1957
9 Sheets-Sheet 5
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May 28, 1963
Filed March 5, 1957
9 Sheets-Sheet 9
United States Patent 0 ice
Robert E. Fearon and Warren G. Ownby,‘ Tulsa, Okla,
assignors to Electro Chemical Laboratories Corpora
tion, Tulsa, Okla., a corporation ‘of Delaware
Filed Mar. 5, 1957, Ser. No. 644,037
11 Claims. (Cl. 324—37)
Patented May 28, 1963
not well adapted to the requirements of pipeline survey
or the survey of oil well casing. Similarly, radiographic
inspection suffers from difficulties. The only type of
radiographic inspection which could be conveniently ap
plied wholly inside a pipe would be the observation of
scattering of suitable radiations. If the suitable radi
ations adequately penetrate the wall of the pipe, and are
properly sensitive to the entire thickness of the pipe, they
have an opportunity to be scattered by the material of
The present invention relates to the testing or inspect 10 the earth which is in contact with it. Because of the
effect due to the material of the earth and because of
ing of metal, and more particularly to a method and
the variation in the density of substance, whether clay,
apparatus for testing or inspecting electromagnetically
sandy soil or stones large and small in contact with the
pipes, tanks, beams and other structures made from a
pipe, errors in measurement of the pipe are brought about.
magnetic material such as iron or steel.
In the art of testing metal structures such as pipes, 15 Such errors in measurement as these cannot be avoided
and cannot be neglected if the method of inspection is
tanks and the like to locate any ?aws which may exist
on the inside or on the outside of such structures, there
are a variety of methods of inspection which are more
The basic object of the present invention has been to
provide a novel and improved method and apparatus for
of merely looking at the metal. To some extent, the 20 logging the conditions in metallic walls of pipes, tanks,
beams and other structures, which method and apparatus
inspection methods which have been developed are of
avoid the di?iculties and eliminate or minimize the de
advantage over merely looking at the metal because they
?ciencies of the procedures heretofore used or suggested.
reveal information that cannot be seen by looking. Also,
or less useful and which replace the elementary procedure
such methods are of advantage for a further reason that
The method and apparatus of the invention involve the
(fall into three categories: (1) sonic inspection in which
faults are recognized by obtaining echoes therefrom, (2)
radiographic inspection in which the ability of the metal
tive magnetometry. Magnetometric methods have here
tofore been employed in surveying the earth, yielding data
they render the data in a systematic form and present 25 principles of magnetometry.
The method of the invention consists basically of a
it quantitatively so that it can readily be compared from
system of measurements based on the principles of sensi
one specimen to the next. In general, such methods
to transmit or to scatter penetrating radiation is the
basis, and (3) magnetic or electromagnetic inspection
which is based on the ability of a mass of metal to react
relevant to local variations and subsurface geologic struc
tures. The practice of the present invention similarly
yields data relevant to structural variations within the
mass of iron being tested and extending throughout the
thickness thereof to and including the side opposite the
side from which the inspection is being performed. A
desirable feature of the magnetic inspection method of
differently to an electromagnetic ?ux if it is ?awed than
it will if it is ?awless.
Certain aspects of the present invention are applicable
the invention is that attention can be directed exclusively
to the testing and inspection of magnetic materials gen
to the iron and the e?ect of materials such as iron rust
erally, others are of particular interest with respect to
can be ignored. This desirable feature results because of
pipes such as are used for transporting oil and gas or for
well casings, and still others are of particular interest with 40 the predominant passage of magnetic ?ux through iron
and because of the fact that a ?ux of magnetic lines so
respect to structures such as tanks, beams and the like
strongly prefers apathway through iron that in certain
which are readily accessible from the outside but not from
reasonable plans and dimensions passage through other
the inside. For convenience, the principles of the inven
nearby materials can be entirely ignored when iron is
tion will be described with particular reference to pipes,
although it should be understood that these principles will
A principal object of the invention has been to pro
be applicable in general to the testing or inspection of
vide a novel and improved method and apparatus for
other structures. The structures With which the present
showing ?aws, pits, loss of iron, local alteration in mag
invention are concerned are magnetic structures, i.e., struc
netic properties of the iron, and to show welds and collars
tures made of magnetic materials such as iron or steel.
and other details of structure which may be or are
In the rapid inspection of pipe underground and in in
accessible places, the known methods of the prior art show
attached to a pipe being surveyed. It is a speci?c object
certain de?ciencies. ~ Some of these de?iciencies are, with
and purpose of the invention to provide means for de
picting these characteristics wherever they may occur
around the periphery of the pipe and to register the oc
?rm contacts must be made in a comparable manner to
arrange the transmission of the sonic waves. Making 55 currence of such phenomena of detail of the pipe with
respect to distance along the pipe and correlate it with
the sonic contacts rapidly and making them exactly the
distance so that the place Where the defect is located can
same and making them all ?rm and effective for the
be identi?ed ‘for repair vor for remedial action of whatever
transmission of sound is di?‘icult in the presence of crusts
kind is desirable or necessary.
and debris which occur inside operating pipelines. Al
Another object of the invention has been the provision
though various procedures exist for cleaning oil and gas 60
of means to determine and indicate whether magnetically
lines and petroleum products lines, still it remains a fact
observable differences on the pipe (indicating flaws, etc.)
that a substantial amount of rust, scale and other'debris
will be found to exist inside the pipes even after the most
occurred on the bottom half of the pipe or on the top
stringent cleaning of any type now available and in com
half of the pipe in a horizontally lying pipe or whether
mon use. For such reasons as these, a sonic method is 65 they occurred on the left side or on the right side facing
respect to the sonic method, that a rapid succession of
in the direction in which the surveying instrument passed
The invention will now be described in greater detail
with reference to the appended drawings, in which:
FIG. 1 is a cross-sectional view of a length of pipe
having a thin place in the wall thereof;
FIG. 2 is a hysteresis loop used for describing mag
netic conditions in the wall of the pipe of FIG. 1;
through the pipe.
A feature of the invention has been the provision of
means employing balanced satura-ble cores to detect the
presence of a weak magnetic ?ux in such a manner that
an even harmonic and a modulation product indicate the
presence of an external magnetic ?eld acting similarly
FIG. 3 is a curve illustrating the response of a detec
tor according to the invention to the ?aw of FIG. 1;
FIG. 4 is a curve similar to that of FIG. 3 illustrating
on both balanced saturable cores.
Still another object of the invention has been the pro
vision of means of observing pipe which so far as pos 10 the response to two oppositely poled widely spaced
magnetic poles;
sible is not critically related to the spacing of the detect
ing instrument away from the iron, but which in general
FIG. 5 is a curve similar to that of FIG. 4 for closely
spaced oppositely poled magnetic poles;
will register chie?y the variations and ?aws which it is
FIG. ‘6 is a sketch illustrating certain principles of
A further object of the invention has been the elimi 15 the invention;
nation of the previous magnetic history of the iron as a
FIG. 7 is a diagrammatic illustration of one form of
factor in the survey. Such previous magnetic history
survey device constructed in accordance with the inven
may arise from a variety of causes, such as the previous
local application of magnets or because of the way the
FIG. 8 is a diagrammatic illustration of another form
section of iron pipe previously lay on a pipe rack or in
of survey device constructed in accordance with the
another pipeline before being assembled into the pipeline
being surveyed. Without such means for removing and
FIG. 9 is a diagrammatic illustration of a survey de
eliminating from consideration the in?ux of previous 10
vice similar to the type illustrated in FIG. 7 combined
calized magnetic disturbances, it is not possible to make
with apparatus in accordance with the invention for re
a reproducible measurement which is representative sole 25 moving the previous magnetic history of a pipe;
ly to variations in the given pipe, but instead the measure
FIG. 10 is a cross-sectional view illustrating a device
ment will, in fact, observe irrelevant data to a consider
.- similar to that of 1FIG. 9, but with a different form
able extent. Such irrelevant data would be representa
of sensing device or element;
desired to measure.
tive of the previous local magnetization, previous assort~
FIG. 11 is a longitudinal cross-sectional view of a
ments of magnetic poles at the ends of sections of pipe 30 ilength of pipe and illustrating one method of practicing
which lay in various ways in the earth’s magnetic ?eld
the invention;
before being assembled together, previous application of
FIG. 12 is a diagrammatic illustration of a survey
device in accordance with the invention employing a
previous contact with highly magnetized mechanical
sensing element of the type shown in FIG. 10 and adapt
tools. vMoreover, the common use of electromagnets for 35 ed to register iron loss over the entire periphery of the
lifting iron in the handling of junk also results in the
presence of peculiar, irrelevant and unpredictable varia
FIG. 13 is a diagrammatic representation of a survey
tions of magnetic characteristics of pipe. Means of re
device similar to the one illustrated in FIG. 12, but with
permanent magnets or electromagnets to the pipe or
moving all these is provided in the present invention.
A feature of the invention has been the provision of 40
‘ sensitivity limited to a particular quadrant or sector;
FIG. 14 is a block diagram of an electrical and mag
netic system for carrying out the invention;
FIG. 15 is a block diagram of a system for graphically
recording the data obtained in the system of FIG. 14;
contained within the survey device.
FIG. 16 is -a block diagram illustrating an arrangement
A further feature of the invention has been the pro
vision of means whereby the data so recorded on a wire 45 in accordance with the invention for accurately recording
the location of a survey device in a pipe;
or the like may be incorporated into graphical ‘form for
FIG. 17 is a longitudinal cross-sectional view of one
detailed observation by removing the record from the
form of magnetic standardizer according to the invention;
survey device at the end of its travel through the pipe
FIG. 18 is a longitudinal cross-sectional view of a length
and by playing the record back through an ampli?er and 50
pipe with a survey device constructed in accordance
demodulator system adapted to produce electrical sig~
with the invention shown therein;
nals which are of the kind required to de?ect the pen
FIG. 19 is an enlarged detail view, partly in cross
means by which the .data pertaining to a pipe survey are
recorded on a wire recorder or similar device wholly
or stylus of a suitable recording device and which are
proportional to the intensity of the signal present on the
section, illustrating the construction of the detecting ele
ment of the survey device of FIG. 18;
FIG. 20 is a longitudinal cross-sectional view of a
An object of the invention has been the provision of
length of pipe containing a different form of survey device
a survey device suitably constructed for propulsion
according to the invention;
through a pipeline under power of the ?uid normally
FIG. 21 is a diagrammatic illustration of the survey
carried by the pipeline, e.g., oil or natural gas.
device of the type shown in FIG. 20 with a block diagram
A further object of the invention has been the pro 60 of the operatingcircuit thereof;
vision of means whereby the survey tool can be prop
FIG. 22 is a longitudinal cross-sectional view of a
wire or other device.
agated through the pipe at a relatively uniform speed
which may be less than the speed of the ?uid being
pumped through the pipe.
length of pipe with another form of magnetic standardizer
and degausser according to the invention located therein;
FIG. 23 is a cross-sectional view of a survey device ac
Still another object of the invention has been the 65 cording to the invention for surveying a flat metal surface;
provision of means for surveying a cased well by pro
FIG. 24 is a sectional view taken along the line 24—24
.ducing and recording an indication of iron de?ciency in
of FIG. 3;
the casing produced by corrosive zones opposite the cas
FIG. 25 is a typical data record showing the survey of
ing. Such recording will be in the detail and in the 70 a length of pipe; and
manner needed to relate such corrosiveness to character
istics of rock formations adjacent to a bore hole.
Other and further objects, features and advantages
of the invention will be apparent from the following
FIG. 26 is a longitudinal cross-sectional view of a
length of pipe with ‘a modi?ed detector according to the
invention located therein.
As indicated previously, before meaningful reproduci
75 ble results can be secured by a magnetic survey of a
metal structure, the structure must be given a standardized
magnetic history or condition. In the case of iron pipe,
a longitudinal ?ux of suitable strength should be created
therein. This may be achieved by passing a magnet
stances. If now a very strong ?ux producing agency acts
in such a manner as to produce a ?ux parallel to the axis
of the pipe and acts in a suf?ciently powerful manner that
through the pipe. The magnet may be of the permanent
all of the iron, both in the section of the iron which is of
full thickness and in the section which is not of full thick
type or it may be an electromagnet. The creation of the
ness, achieves relatively complete magnetic saturation,
standardizing ?ux in the pipe may take place prior to or
contemporaneously with the passage of the survey device
then certain conclusions proceed. ‘If we assume that
after the magnet has passed, the next condition which
through the pipe. To erase magnetic history and to pro
will prevail is a condition in which the value of the vec
vide a magnetic condition in which the pipe will yield 10 tor H parallel to the axis of the pipe is substantially zero,
maximum information to the survey device, the magnetic
then considering an absence of free poles (a condition
standardizer should be made from a suitable magnetic
which would be ful?lled on very long uniform pipe),
material and with suitably shaped pole pieces to deliver
the iron will fall back on the hysteresis loop exhibited
to the pipe walls a very strong magnetic flux. It has been
in FIG. 2 to a point where the left-hand branch of the
found desirable in most cases for the ?ux to approach
loop intercepts the B axis. Assuming that all the iron
that at which magnetic saturation of the iron will occur.
of the section illustrated in FIG. 1 does, in fact, fall
In common grades of mild steel, for example, the chief
back to the point shown, then we can compute through
component is elemental iron, and magnetic saturation will
the section act and the section bb in FIG. 1 what is the
occur with a ?ux density in the order of 19,000 lines per
surface integral ‘of lines (that is, the total magnetic flux)
square centimeter. In general, in the practice of the in 20 proceeding from left to right through the ‘full thickness
vention, it is preferable to employ a magnetic flux which
section and through the thinned section, respectively. If
is of suf?cient strength to insure complete eradication of
the full thickness section has an area of X square cen
the effect of former magnetic occurrencies, i.e., magnetic
timeters and the thinned section has an area of Y square
history. A ?ux density at which magnetic saturation oc
centimeters, as exhibited in the planes aa and bb, respec
curs will ensure this complete eradication of magnetic 25 tively, and if X is greater than Y, then we may write
history. Under some conditions of testing it is not only
desirable to eradicate previous magnetic history from the
pipe, but to also leave the pipe in a weak magnetic state
or degaussed. This may be done by passing through the
pipe either an A.C. excited electromagnet or alternately
and in succession oppositely polarized magnets, each of
that the flux under the conditions of relaxation of ?eld
as given previously through the thick section B0X=¢o
for the thick section and B0Y=¢1 for the thin section,
since X is greater than Y, the ?ux ¢0 is greater than the
flux Q51. Since, however, ?ux must be continuous through
which has a magnetizing strength weaker than the one
preceding it. Such an arrangement will result in a condi
nated anywhere in view of the general theory of mag
netism, this condition can only exist if the extra portion
of the ?ux which corresponds with the thick section passes
through the air or through space adjacent to the thin sec
tion to maintain continuity. Again, as is expected in the
theory of magnetization, there will be regions in the
vicinity of the thinned section where the ?ux enters and
tion of the iron which corresponds with equilibrium of
the iron structure with the magnetic ?eld of the earth.
Such a magnetic condition is achieved by generally sim
ilar means by the so-called degaussing procedures. In
the use of weaker ?elds not corresponding with total
out space and magnetic flux cannot be absorbed or elimi
saturation of the iron, the requirement is simply that the
leaves the zone where the thinning down occurs on both
?eld be strong enough to overcome previous magnetizing 40 sides of the thinned section. As would be expected, the
processes which may have occurred and remove the
e?ects of these so far as they still remain in the iron.
How strong a magnetizing ?eld may be required to erase
such previous effects depends somewhat on how strongly
zone where the flux leaves has the characteristics of a free
pole and the zone where it re-enters the iron has the
characteristics of a free pole of opposite polarity and
equal total ?ux strength. Accordingly, in view of these
the previous disturbances were impressed upon the iron. 45 considerations, a flaw in the iron will exhibit itself as an
In general, unless powerful electromagnets were used or
alternate system of two magnetic poles. The presence of
other extremely potent magnetizing effects were used on
such magnetic poles will be observed and recorded by the
the pipe being tested, a magnetic pole adapted to afford a
detector or sensing element of the invention. A possible
longitudinal ?ux of 1000 lines per square centimeter lon
detector response to a single pole where the opposite pole
gitudinally in the pipe should suffice to erase the results
is very remote is shown in FIG. 3. Such a response to a
of previous disturbances. It is believed that weaker ?uxes
succession of two opposite poles spaced apart a short
than this will not be satisfactory and it is preferable to
distance is illustrated in FIG. 4. FIG. 5 shows such a
use stronger ?uxes.
response for two opposite poles spaced close together. In
In addition to achieving a standardized magnetic con
dition, the invention involves the sensing and recording
of magnetic discontinuities in the metal walls being inves
tigated. Such discontinuities can arise because of
a loss of metal, for example, from corrosion; because of
the addition of metal, for example, from welds; because
of flaws in the metal; and from the structure of the metal,
for example, the presence of collars and other structural
details. These magnetic discontinuities give rise to
phenomena susceptible of sensing and measurement, as
will be described in considerable detail hereinafter. How
ever, ?rst there will be discussed the magnetic phenomena
existing because of such a local unusual condition in the
Considering ?rst FIG. 1, there is shown a section
through an iron pipe 30' having a thin wall portion ex
FIGS. 4 and 5 the pole pitch may be considered as ex
tending from the maximum to the minimum, one rep
resenting la north-seeking pole and the other a south-seek
ing pole. The curve of FIG. 5 may be considered typical
for a single isolated flaw as identi?ed by the apparatus
to be described in connection with FIG. -12. If the mag
netic ?ux passes through the iron in the direction in
dicated by the arrows in FIG. 1, a north-seeking pole will
be set up adjacent the point 31, while a south-seeking pole
will be set up adjacent the point 32. Similar but much
weaker poles Will result from the presence of relatively
weak ?uxes, such as that resulting from the earth’s mag
netic field.
It should be understood that magnetic poles indistin
guishable from those caused by the earth’s magnetic ?eld
acting on a flaw could be created by magnetic disturb
tending from the point 31 to the point 32 and which might 70 ances unrelated to discontinuities in the iron. Since such
be created in actual conditions by corrosion. The pipe
magnetic poles would produce records which would ob
walls on both sides of the section 3l—32i are of full thick
scure a log of the pipe, it is desirable that they be elimi
ness. The thin place which is illustrated may or may
nated by creating a standardized magnetic condition in
not extend entirely around the periphery of the pipe,‘ and
the iron. Use of a strong ?eld to effect the standardized
the following discussion will be applicable in both in 75 condition will also enhance the formation of poles mark
ing conditions in the iron whose presence it is desired to
the vicinity of the outwardly projecting portion of 56 is
FIG. 6 illustrates generally the basic principle of one
receptive to ?uxes originating in the pipe, and which may
form of the invention, although it should be understood
These ?uxes originating in the pipe are in a direction ‘gen
erally perpendicular to the direction of motion of the
that this ?gure does not purport to show a working de
vice. In FIG. 6, there is shown a magnet 40 having north
and south poles arranged .so that the flux will enter and
leave according to the arrows. The magnet 4%‘ may be
of the permanent type or it may be an electromagnet.
When the magnet 40 is placed in a pipe it produces a 10
longitudinal, i.e., axial, ?ux in the pipe walls. A sensing
element 41 is provided which is responsive to weak mag
indicate the presence of ?aws or other anomalies therein.
sensing device. In the embodiment of FIG. 7, the ?ux
path will be ‘limited generally to a narrow arc of the pipe
periphery determined by the radial position of the coils
54, 55 and their respective cores. The reluctance of the
inward and outward magnetic paths will be different
Whenever the characteristics of the iron for one path differ
from the characteristics of the iron ‘for the other path.
netomotive forces and is arranged to be sensitive in a
For example, a ?aw in the iron, at weld or a collar will
direction perpendicular to the longitudinal ?ux produced
by the magnet 40. If the environment of the sensing
system is magnetically homogeneous, no magnetomotive
produce a local magnetic pole, as described. The pres
ence of such a pole creates an asymmetrical magnetic
condition such that a net radial magnetomotive force will
be produced at even harmonics. For a sinusoidal input
force will be exerted on the sensing element 41 since its
poles lie in the equatorial plane of the magnet Kit). When
a disturbance exists, such as, for example, is produced
by local poles caused by ?aws and the like, a magnetomo
tive force will be exerted ‘on the element 41. Local dif
ferences of permeability in the magnetic structure being
surveyed will set up local poles because of the axial mag
netic ?eld from the magnet 40, and these local poles will
signal, the second harmonic will be the predominant har
However in order to achieve a substantial har
monic content with a sinusoidal input signal, the input
signal to the coil 5§ should be of su?icient strength to
saturate the core 56, so that the E.M.F.’s induced in the
windings 54 and 55 will be distorted. While complete
saturation is not indispensable, the core 56 should be
cause a magnetomotive force to be exerted on the sensing 25 operated in a range in which it will exhibit non-linearity.
element 41.
FIG. 7 shows a sensing device separate from the stand
In general, the greater the non-linearity the better will be
the operation.
ardizing magnet. In this ?gure, which is exploded for
The net radial magnetomotive {force sets up a net
clarity, there is provided a non-magnetic core 45 having
in the side coils 54- and 55. The coils 54 and 55
?anged ends 46 and 47 whose diameter is such that the 30 may be connected together in series or in parallel, so
long as their directions of winding are opposite or in
periphery of the ?anges approaches the interior pipe sur‘
other words so long as they link the ?uxes in opposite
face when the device is located in the pipe. The core
45 and the ?anges 46' and 4'7 do not enter into the mag
directions. The net
may be ?ltered, ampli?ed
netic circuit to be described and hence may be made of
‘and recorded, as indicated in FIG. 14. In this ?gure,
any suitable non-magnetic material. A forward end 48 35 an oscillator 6t?‘ supplies alternating current to the exciter
may be af?xed to the ?anged end 47 and may be con
coil 59 of the magnetometer system 61, which may be of
the type just described. The net
in the coils 54
structed, in a manner to be described hereinafter, to fa
cilitate passage of the sensing device through the pipe.
and 55 is supplied to- a ?lter 62, which may be tuned to
A rear end 49 may be a?ixed to the ?anged end 46 and
the second harmonic of the frequency supplied by the
similarly may be constructed to facilitate passage through 40 oscillator 6d. The output of the ?lter 62 is ampli?ed in
the pipe. The end 49 may conveniently carry the neces
an ampli?er 63‘ and recorded on a suitable recording
sary electronic components of the sensing device.
device ‘64. The recorder 64 is preferably of the wire or
A magnetic core 50 has ‘a central portion 51 parallel
tape recorder type since the physical size of this type of
to and supported by the core 45. The portion 51 may
recorder is relatively small for a given capacity, and hence
be imbedded in the core 45 for mechanical support. 45 is most conveniently incorporated in the sensing device.
Radially extending ends or legs 52 and 53‘ of the core 50
The elements 6944 may be mounted in the end 49.
carry windings 54 and 55, respectively. Another core
After the sensing device has traversed the pipe length to
56 of saturable magnetic material having radially extend
be tested, the wire may be removed from the recorder 64
in-g legs 57 and 58 is (located symmetrically between the
‘legs 52 and 53. The legs 57 and 58 are joined at both
ends to [form a complete magnetic path. The legs 57 and
and placed in a playback set 65 (FIG. 15). The output
of the set $5 is demodulated in a conventional linear de
modulator 66, which may be of the simple diode or recti
?er type, and the resultant signal is recorded for visual
58 carry a coil 59, as shown. The bottom legs of the
core 56 is parallel to and adjacent to the 1leg 51 and is sup
observation on a graphic recorder 67. A typical data
ported by the core 51.
record is illustrated in curve A of FIG. 25. Where it is
If the center coil 59 is supplied with a suitable alter 55 convenient to have a wire line connected to the sensing
nating current, e.g., a sinusoidal 750 cycle signal, an al
instrument, for example when surveying a, well casing or
ternating ?ux will be set up in the cores 56 and 5-1. This
an easily accessible pipe, the local recorder may be
?ux will ‘have an axial (i.e., parallel to the leg 51) com
omitted and the signal transmitted over the wire line to
ponent which will tend to produce equal electromotive
a ‘graphic recorder at a remote location.
forces in the side coils 54 and 55. These side coils should 60
The structure of FIGURE 7 can be modi?ed by re
be wound in opposite senses and connected so that the
placing the coils 54 and 55 with a single coil (not shown)
E.M.F.’s ‘generated thereby will be of opposite polarity.
wound around the core 56 with each turn encompassing
The magnetic ?uxes produced in the legs 52 and 53' link
both legs 57 ‘and 58. The net
set up in such a
the side coils 54 and 55. These ?uxes are caused by the
coil will be equivalent to the net
set up in both
?uxes ?owing in legs 57 ‘and 58, and leaking therefrom
coils 54 and 55.
through the leg 51. An important characteristic of the
The sensing structure of FIGURE 7 is responsive to
?uxes in the legs 52 and 53‘ is that the fundamental, e.g.,
magnetic anomalies occurring over a limited extent of
750 cycle, component always cancels out, but the second
the periphery of the pipe. Additional sensing structures
harmonic, e.g., 1500 cycle, component due to harmonic
may be provided to increase the arc of the pipe periph-,
generation in the iron of structure 56 does not always 70 ery being tested. Such additional structures would be
cancel out. In fact, the magnitude and relative phase of
spaced angularly from the structure shown and may have
the 1500 cycle component is responsive to net ?ux enter
corresponding coils connected in parallel.
ing 56 ‘from the metal structure being tested, i.e., along
the top leg of the structure 56, and leaving where it lies
The sensing device of FIGURE 7 is eliectively a mag
netic ampli?er in which modulation is produced in ac
closest to leg 51.
When the instrument is run in a pipe, 75 cordance with magnetic anomalies existing in the struc
ture being tested. Such an arrangement is preferred
since the energy levels of signals produced in response
to magnetic anomalies may be relatively high. However,
a self-generating type of sensing device may be used in
of sensing device 82. Under actual operating conditions,
the standardizing magnet will usually be caused to pass
through the pipe length completely prior to insertion of
the sensing device in the pipe.
some cases. Such a device is illustrated in FIGURE 8.
In FIGURE 8, an E-shaped magnetic core 68 corre
A sensing device of the type shown in FIG. 10 but
without the permanent magnets is illustrated in FIG. 12,
sponding to the core 50 is provided. Coils 54, 55 and
which is exploded longitudinally for clarity. In FIG. 12
a hollow soft iron core 83 is provided with soft iron,
?anges 84 and 85 whose radii are slightly smaller than
the pipe radius. The term soft iron, as used herein,
leg of
in the
the core
55 and
the pipe.
5S, as The
a result
net of the 10 means magnetically soft. ‘Coils 86 and 87 (correspond
ing to the coils 71 and 72) are wound on the core 83.
motion of the core 68 through the pipe will vary as the
A coil 88 provided with a steel tape wrapping 89 is
derivative with respect to time of the net radial mag
59 are wound on respective legs of the core 68 in a sense
to aid each other with respect to the ?ux entering the
netomotive force and hence will be sensitive to the ve
wound about the core 83 between the coils 86 and 87.,
will be 15 In this case, the flux paths to the pipe walls include the
?anges 84 and 85. The ?anges 84 and 85 act to limit
generated in the coils as a result of the unchanging axial
the detecting zone near the periphery of the sensing de
?ux in the pipe since such ?ux will be cancelled out in
vice to a region of space ?aring outwardly from the
the core 68. Only radial ?uxes, resulting from mag—
longitudinal axis of the sensing device. The greater the
netic anomalies, will produce an output
output may be ampli?ed and recorded to yield a log. 20 radius of the ?anges 84 and 85 and the closer these
locity of the sensing device. No net
It will be evident that either the coil 5% or the coils 54
and 55 may be omitted.
FIG. 9 is a diagrammatic illustration of a survey de
vice similar to that of FIG. 7. In FIG. 9 there are pro
vided permanent magnets 69 and 70 of the radial type. 25
?anges come to the coils 86 and 87, the more limited will
and 72.
as many places as desired around the circumference of
be the boundaries of the detecting zone and the sharper
will be the response of the instrument to magnetic
anomalies. In other words, when the ?anges 84 and 85
approach in radius the internal pipe radius and when
these ?anges are closely spaced axially with respect to
The axial spacing of the permanent magnets 69 and 7!}
the coils 86 and 87, the output pulses plotted with re
should be sufficiently great that tilting of the device will
spect to movement of the instrument along the axis of
not unduly distort the standardizing magnetic ?eld. The
the pipe will have steep sides, which facilitates accurate
peripheries of these magnets should be of opposite po
larity to create a strong standardized axial magnetomo 30 determination of the location of the magnetic anomalies,
with respect to the pipe length. The ?anges 84 and 85(
tive force in the pipe. This unvarying magnetomotive
may be reduced in size or omitted, but this is not pre
force creates, in e?ect, a standardized magnetic history
ferred since the region of sensitivity will be broadened,’
in the iron. Instead of having the magnetic staudardizer
tending to make log interpretation more di?icult.
pass through the pipe in fixed relation to the sensing de
Since generation of an appreciable net
in the
vice, as in FIG. 9, it is preferred to pass a magnetic 35
coils 86 and 87 is dependent on saturation of the steel
standardizer through the pipe in advance of the sensing
tape 89 (one side of which becomes saturated more rapid
means, as is illustrated in FIG. 11. The magnetic stand—
ly than the other upon presence of a free pole in the
ardizer may be passed through the pipe any desired time
magnetic path of the ?ux passing therethrough) detection
in advance of the sensing means, the only limitation be
ing that the time not be so long, having regard to the 40 of ?aws or other magnetic anomalies in the pipe walls
‘can be restricted to any desired arc of the pipe periphery.
location of the pipe, that local magnetic conditions in
Thus while the steel tape 89 in FIG. 12 extends all the
the pipe are likely to change.
way around the coil 88 and hence core 33 in FIG. 12 and
The combined sensing and wiping means of FIG. 10
thus provides detection through an arc of 360°, the steel
is similar to that of FIG. 9. However, in the case of
FIG. 10, the coils 71 and 72 corresponding to the coils 45 tape 89 in FIG. 13 is limited to a much smaller arc and
hence detection of magnetic anomalies is correspondingly
54- and 55, respectively, are wound directly on the soft
limited to substantially the same are of the pipe circum
iron core 45. The coil 73, corresponding to the coil 59
ference. The magnetic material tape may be provided at
is similarly wound on the core 45 between the coils 71
Soft iron ?anges 52’ and 53' are provided on
respective sides of the coils 71 and 72. The coil 73 is 50 the core 83 to provide detection in corresponding arcs of
the pipe circumference.
wrapped with a saturable steel or other magnetic mate
The net electromotive force in the coils 86 and 87
rial tape 74. The flux set up as a result of the exciting
may be ?ltered (to pass the second or other selected even
current supplied to the coil 73 saturates the tape 74 so
harmonic), ampli?ed and recorded, as illustrated in FIG.
that it acts as a non-linear reluctance element analogous‘
to a recti?er used as a modulating element. In the pres 55 14. The graphic reproduction of the recorded data,
produced as shown in FIG. 15, may look like the curve A
ence of an ambient magnetic ?eld, such as is caused by
of FIG. 25 in which magnetic anomalies appear as pips
the presence of a ?aw in the pipe, the tape on one side
or departures from the average value. The extent and
of the coil 73 becomes saturated more rapidly than the
amplitude of the pips will, of course, be dependent on the
tape on the other side. A net
will be induced
in the side coils 71 and 72 because of the resulting un 60 characteristics of the anomaly.
For the curve A of FIG. 25 to vbe useful, it is necessary
equal reluctance of the outgoing and incoming radial
to know as closely as possible the physical location of the
?ux paths. These radial ?ux paths include a respective
side of the tape 74, i.e., the left and right sides as shown
in FIG. 10 and ?anges 52.’ and 53'.
anomaly on the pipe corresponding to each pip. If the
velocity ‘of the sensing device in the pipe were absolutely
The frequency response of the recording device limits 65 uniform, then thephysical location of the ?aw or other
anomaly would be directly proportional to the location of
the frequency of the alternating current which may be
the pip on the time axis of the curve. In general, how
supplied to the coil 73-. If the recording device has a
su?iciently high frequency response, high frequency sig
ever, such an ideal condition can not be exactly achieved.
However, in accordance with the invention, means is
nals may be used. In such case a ferrite material might
be desirable for the tape 74.
70 provided for producing indications on the record corre
sponding to physical progress of the sensing device. One
The permanent magnet ?anges 69 and 70 of FIGS. 9
such means is illustrated in FIG. 16‘ and may conveniently
and 10 need not be used if a standardizing magnet is,
sent through the pipe in advance of the detecting device.
be located physically in the ends 48 and 49 of the sensing
This is illustrated in FIG. 11 in which a magnetic stand
ardizer 80 is shown passing through pipe 81 in advance 75 In FIG. 16, there are provided two electromagnets 90
and 91 separated by a desired axial distance‘and located
in the same axial plane. The magnet 90, which may be
termed the marking magnet, is preferably located adjacent
the front or leading end of the sensing device, while the
magnet 91, which may be termed the pickup magnet, is
preferably located adjacent the rear or trailing end of
the sensing device. The magnet 90 is constructed and
located so that each time its coil is provided with a sharp
impulse of current, a corresponding spot on the adjacent
pipe wall is magnetized. The poles of the magnet 90‘ 10
should be oriented so that the magnetized spot will have
little or no ?ux extending in a longitudinal direction, since
such longitudinal ?ux would look to the sensing element
as a ?aw or other magnetic anomaly. A peripheral ?ux,
prises a soft iron core 96 having radial permanent mag
nets 97 and 98 mounted thereon adjacent respective ends
thereof. The periphery of one of these magnets should
be a north pole while the periphery of the other should be
a south pole in order to set up an axial ?ow of ?ux
through the pipe walls as the device passes through the
pipe. The magnets ‘96 and 97 preferably have a high
coercive force to resist self-demagnetization. While the
diameter of the permanent magnets should be approx
imately that of the internal diameter of the pipe, it is de
sirable that ‘some gap be provided to minimize attraction
between the magnets and the pipe walls. Non-magnetic
sleeves >99 and 109 may be used to ensure a minimum
ing element. The pickup magnet 91 is oriented in the
air gap. The space between the magnet-s 97 and 98 may
be ?lled with any suitable material, such as a plastic 18!.
A number of threaded studs 102. project from the walls
same way as the magnet 99 so that a voltage will be
induced in the coil of the magnet 91 as it passes the mag
and 104.
on the other hand, will have little or no effect on the sens
of the magnets 97 and 98 for affixing guide members 1163
The guide member 103‘ is formed as an annu
netized spot laid down by the magnet 9G. The voltage
lar washer having a vertical portion v105, which is clamped
induced in the coil of the magnet 91 is ampli?ed in an 20 in place between annular metal washers 1% and 107, and
ampli?er 92 and is supplied to the electromagnet 90 to
' a rearwardly extending ?ange portion 107 which is adapted
cause the latter to lay down another mark which in turn
to be in sliding contact with the pipe walls. The washers
will be picked up by the electromagnet ‘91. It will be
106 and 107 are held in place and in clamping relation
evident that the spacing between marks is dependent only
ship to the washer 103 by nuts 108 threaded on the studs
on the spacing between the magnets 99‘ and 91 and not on 25 102. The face 109 of the washer 106 is made solid to
the velocity of the device in the pipe. The current pulse
prevent the passage of ?uid except through a central open
which lays down the mark is preferably very sharp so as
ing 110. A U-bolt 1111 may be provided in the washer
to accurately locate the marks and also to prevent any
106 to facilitate handling of the device. The rear guide
appreciable axial ?ux component from the marks. For
104.‘- is similarly constructed except that both of the metal
this purpose, the ampli?er 92 is preferably of the non
washers are open except for the guide clamping faces.
linear peaked type.
tln operation, the device is placed in the pipe with the
. The ampli?ed output of the ampli?er 92 is also supplied
washer 163 leading and with the flange portions of the
to an oscillator-modulator stage 93. The oscillator car
washers 163 and 194 in contact with the pipe walls. The
rier frequency is modulated by the output pulses of the
?uid, e.g. oil or gas, traveling through the pipe exerts a
amplifier 92. This modulated carrier is supplied to the 35 force on the rear end of the device, causing it to travel
recorder 64. The carrier frequency should be selected
along the pipe. Some ?uid enters through the holes in
the rear annular ‘washers, passes around the outside of
so that, with its sidebands, it is outside the range of the
sidebands of the detector carrier supplied to the recorder
the sleeves'99, 1% and 101 and passes out through the
opening 110, so that the velocity of the device will be less
64 by the ampli?er 63 (FIG. 14). The recorded signal,
when graphically reproduced (as in FIG. 15) results in 40 than that of the ?uid. If desired, the size of the opening
116' may be adjusted to vary the speed of the device. In
a separate information carrier with periodic pips, as
shown by the curve B of FIG. 25. Each of the simple
some cases, especially for smaller diameter pipes, it will
pips of the curve B represents an equal axial travel of the
be desirable to provide a longitudinal hole in the soft
iron core 96 to permit passage of ?uid.
device. The actual spacing of the pips in the time scale
Another practical form of standardizing device for eradi
may vary, as illustrated, because of changes in velocity of 45
cating magnetic history in a pipe and degaussing is illus
the device in the pipe.
trated in FIG. 22. ‘In FIG. 22 the standardizing device
As described, the distance between adjacent simple
has a hollow soft iron core ‘112 supported from ?anges
pips on curve B is equal to the spacing between magnets 90
,113 and 114 carried by platforms 115 and 11.16, respective
and 91. If a different scale should be desired, the ampli
fier 92 could be constructed so as to cause marks to be 50 'ly. The platforms 115 and 116 are provided with wheels
or casters 117 arranged to be in contact with the pipe
laid down at multiples of the distance between the mag
walls 118 for supporting the device in the pipe. The soft
nets. The initial marking impulse as the sensing device
travel commences can be provided externally.
The facilitate correlation between pips on curve A of
iron core 1112 carries spaced radial permanent magnets
1119, 120 and 121, the peripheries of which are succes
FIG. 25 and speci?c physical places on the pipeline, suit 55 sively oppositely poled. The magnets 119, i120 and 121
are provided with non-magnetic sleeves ‘119’, 120’ and
able benchmarks may be provided at known positions
1121', respectively. Sleeve .120’ is thicker than sleeve
along the pipe, for example, at stream crossings or the
M9’ and sleeve 121’ is thicker than sleeve 120’ so that,
like. A suitable benchmark could be produced by mag
if the magnets are of equal strength, the increasing gap
netizing a point on the pipe with a strong magnetomotive
force or exposing a point on the pipe to a gamma ray 60 will cause less ?ux to pass into the iron from the succes
source. The orientation of the benchmark, with respect
to the periphery of the pipe, if a magnetic mark is used,
is preferably such as to be a considerable angular distance
sive magnets. In this way the magnet ?eld set up be
tween the magnets 119 and 120 will be followed by a
weaker and recessed ?eld set up between the magnets 120
and 121, which has been found to be a desirable way to
from the marks laid down by the magnet 96. A detector
94 is provided to sense the presence of the benchmarks 65 achieve magnetic history removal along with degaussing.
If desired, more magnets may be provided to control fur
and to produce a distinctive modulation on the carrier
ther the relaxation of the degaussing ?eld. 1Also, mag
generated by the oscillator 93. For example, the detec
nets of equal diameter but successively decreasing strength
tor 94 could shock excite the oscillator tank circuit to
produce a transient modulation as indicated at 95 in FIG.
may be used.
The deg-aussing device of FIG. 22 is forced through the
25. The benchmark modulation record is preferably 70
pipe 118 by action of the ?uid on the platform 116.
such as not to obscure the position indications resulting
Fliud may be passed through the hole in the core 112 to
from pick up by the magnet 91.
FIG. 17 illustrates a practical magnetic standardizing
reduce the velocity of the degaussing device, and a dia
phragm may be provided to control the effective diameter
device, according to the invention, for achieving a stand
ardized magnetic history. The device of FIG. 17 com
of the hole and thus provide velocity control in a manner
responsive to the speed of movement of the instrument
relative to the pipe. A suitable soft rubber or other
gasket may be provided to prevent passage Of ?uid past
the periphery of the platforms 115 and 116. If desired,
the space between the platforms and/ or the magnets may
be ?lled with a non-magnetic material.
tion are applicable to the surveying of cased wells since
corrosion of the casing and hence the thickness of the
casing wall from point to point is dependent on the
character of the surrounding strata so that a log showing
the corroded areas of the casing will yield desired infor
mation on the character of the earth formations surround
While the magnetic standardizing devices illustrated
have been shown as using permanent magnets, electro
ing the well from point to point.
As pointed out previously in connection with FIG. 13,
the magnetic tape 89 or 89’ may be omitted over one
magnets can of course be used. In such case local battery
power or, where appropriate, cable transmitted power, can 10 or more arcs of the pipe periphery in order to restrict
detection of anomalies to a selected are or arcs opposite
be used for magnet excitation. A standardizing electro
the tape wound portion or portions. Two or more sepa
magnet using alternating current excitation will achieve a
standardized magnetic condition provided the excitation
frequency is sui?cien-tly low to penetrate the iron walls,
rate assemblies of elements arranged to log different arcs
of the pipe circumference may then be used. For ex
e.g. two to ?ve cycles per second for most pipes.
15 ample, one assembly could be used to survey the entire
circumference to show particularly welds, collars and
While standardization of the iron may be effected
other large discontinuities. Another assembly could be
through the use of high ?ux densities to achieve substan
used to give particular attention to corrosion in the bot
tial saturation, as previously described, a somewhat lower
tom zone of the pipe. The construction of FIG. 19 can
?ux density may be used to achieve a standard equilibrium
condition in the iron by subjecting the iron to successive 20 be used to provide two sensing channels by providing
two steel tape wrapped coils 88’ (not shown) and ex
reversals of magnetic polarity, as with the apparatus of
citing each of these coils with a different exciter fre
FIG. 22, ‘although the successive ?elds need not decrease
quency. The exciter second harmonic frequencies should,
in strength. Subjection of iron to successive reversals of
in such case, be widely separated to permit convenient
magnetic ?elds achieves a cyclical equilibrium. Use of a
separation by ?ltering before demodulation. The steel
standardizing ?eld of saturating strength, as with the ap
tapes should be isolated from each other to reduce any
paratus of FIGS. 9 and :10, may be considered as the lim
tendency for inter-modulation to occur.
iting case in which the ?eld ‘is suf?ciently strong that cy
Plural channel sensing may also be achieved with con
clical equilibrium is achieved with a single reversal of
structions of the type shown in FIGS. 7 and 8 by pro
polarity. Cyclical equilibrium achieved with reversals of
successively decreasing ?eld strength will leave the iron 30 viding a plurality of angularly spaced sensing elements.
in a degaussed condition, i.e., with a small or zero mag
In accordance with a further aspect of the invention,
a modi?ed method and apparatus for sensing magnetic
anomalies in iron will now be described in connection with
rium with the earth’s magnetic ?eld, which is the usual
FIGS. 20 and 21, FIG. 21 being a block diagram and
degaussed condition of a large mass of iron.
Referring now to FIGS. 18 and 19, there is illustrated 35 FIG. 20 representing a practical construction. Referring
now to FIG. 21, an electromagnet 130 having a core ‘131,
one practical form of construction for a sensing device ac
spaced pole pieces 132 and 133 and exciting coils 134 and
cording to the invention. The particular sensing device
135 is located within a pipe 136 and arranged to tra
shown is of the type illustrated in FIG. 12. In FIG. 18,
verse the pipe in an axial direction. The faces of the
the pipe is shown at 122. Wheeled spaced platforms 123
and v124', similar to the platforms 115 and 116 of FIG. 40 pole pieces 132 and 133 are located so that the pipe
walls will be included in the magnetic circuit.
22, ‘are provided to carry the sensing device through the
The coil 135 is supplied with alternating current at a
pipe 122. A core 125 extends between the platforms 123
In the case of a pipe, the iron is left in equilib
and 124. The core 125 is preferably hollow to permit the
?ow of ?uid therethrough and is preferably made from
frequency J‘ from a suitable source 136’. The resultant
?ux set up in the electromagnet 139 should be sui?ci
ently strong to saturate the pipe walls between the pole
non-magnetic material.
The'core 83, the ?anges 84 and 85, the coils 36, 87 45 ‘faces. However, the ?ux should not be strong enough to
and 88 and the tape 89 of FIG. 12 are designated with
similar but primed reference numerals in FIGS. 18 and
The core 83’ is mounted on the core 125 at an
saturate the core 131 or the pole pieces 132 and 133 since
these should be operated on the linear portions of their
hysteresis loops. To ensure complete saturation of the
pipe iron throughout its entire thickness, the frequency i
intermediate position. The coils 86', 87' and 88’ are pro
vided with non-magnetic covers 861", 87" and 88", re 50 should be relatively low and may be of the order of two
to ?ve cycles per second for usual pipe wall thicknesses.
spectively. The coils are mounted in a U-shaped annular
Saturation of the pipe iron in the magnetic circuit in the
magnetically soft iron sleeve 83", which ?ts into a corre—
presence of an ambient magnetic ?eld in the pipe iron re
sponding socket in the non-magnetic core 83’. The tape
sults in a non-linear load on the coil 135, in turn dis
89’ is preferably an easily saturable magnetically soft
torting the waveform of the voltage supplied thereto.
iron. It might be, for example, .001” thick. The spac
This distorted waveform will have a high even order
ing between the ?anges of the sleeve 83" and the inside
harmonic content with the second harmonic predominant.
surface of the pipe 122 is somewhat exaggerated in FIG.
The saturated iron acts as a non-linear reluctance ele
18, since the air gap therebetween should be much smaller
ment (in much the same manner as the steel tape 89 of
than the axial spacing between the ?anges of 83". A
compartment 49’, located adjacent the sensing elements, 60 FIG. 12) and intermodulaticn of the ambient ?ux and
alternating flux results in the harmonic generation. The
may be used to carry the electronic components of FIGS.
second harmonic of the voltage from the source 136" is
14 and 16 and a suitable power supply. The detecting
passed through a tuned ?lter 137, is then ampli?ed in a
and marking elements of FIG. 16 are not shown in FIG.
peaked ampli?er 138, is adjusted in phase by a phase ad
18, but may be located at any suitable place, preferably
juster 139 and is supplied to one phase winding of a two
adjacent the ends of the sensing device. Propulsion of
phase motor 140. The signal from source 136 is also
the sensing device is accomplished in the same manner
supplied to a frequency doubler 141 which delivers a.
as described for FIG. 22. For logging an empty pipe,
double frequency signal of ?xed phase to the other phase
some or all of the wheels may be powered. For logging
of the two phase motor 140‘. The phase adjuster 139 is
a cased well, the device will be raised and lowered ver 70 employed to- ensure that the ampli?ed 2]‘ signal (from
tically by a wire line. Signal information from the de
ampli?er ‘138) will be in phase or 180° out of phase with
vice may be transmitted via cable under certain con
the 2f signal from the frequency doubler. The phase of
ditions where convenient and where the recording and
the ampli?ed 2]‘ signal will be dependent on the direc
playback would be a handicap.
tion of the ambient ?eld present in the pipe iron. If
It should be observed that the principles of the inven 75 the ambient ?eld in the pipe iron is zero, there will be no
ampli?ed 2]‘ signal and the motor 140 will not operate.
tor 148, the output of which is supplied to wire recorder
An ambient ?eld in one direction will produce an am
pli?ed 21‘ signal in or out of phase (as the case may be)
with the double frequency signal, resulting in motor op
eration in one direction.
An ambient ?eld in the other
direction will produce an ampli?ed 2]‘ signal of opposite
phase, resulting in motor operation in the other direc
The motor 141) operates the slider of a potentiometer
As indicated previously, a number of harmonics will
be created in the waveform of the source 136 in the pres
ence of an ambient ?eld in the pipe iron between the pole
pieces 132 and 133. One of these harmonics (preferably
the second) can be used to achieve a null, as described.
However, other harmonics and particularly harmonic
ratios can be used to provide valuable information as to
1412. The slider of potentiometer 142 is connected to one 10 the character !of the magnetic anomaly detected. Har
terminal of coil 134. The other terminal of coil 134 is
monics caused by a hysteresis loop of the pipe iron (odd
connected to the junction of series connected D.C. cur
harmonics) will be a function of the thickness of the iron
rent sources 143 and 144, the opposite ends of which are
and also of the type of iron and thus ‘will show changes
connected to respective ends of the potentiometer 142
in iron structure such as may be caused by welding. The
winding. The ?ux passing through the pipe as a result 15 ratio of second to third harmonic is useful in interpreta
of the DC. current ?owing through coil 134 is in a sense
tion of the log. A record of the third (or other harmonic)
to oppose the ambient flux in the pipe. Motor 145) will
can be ‘obtained by means of a tuned band pass ?lter 149
continue to move the slider of potentiometer 142 until the
the output of which is used to modulate the carrier gen
net D.C. ?ux is reduced to zero, i.e., until the ambient
erated by an oscillator-modulator 150, the modulated
?ux in the pipe is balanced by an equal and opposite ?ux 20 carrier being recorded by the wire recorder 15. The
from the coil 1134.
separate carrier frequencies from the oscillator~modula~
Prior to passing the electromagnet 139‘ through the
tors ‘144, 148 and 156‘ should be su?iciently separated to
pipe, a degausser should be passed therethrough to eradi
prevent overlapping of their respective sidcbands.
cate previous magnetic history and to reduce the residual
induction to a very low value.
In the practical construction of FIG. 20, the coils 134
t is preferable to use a 25 and 135 are wound one above the other, the adjacent
degausser of the type illustrated in FIG. 22 which will
turns being separated by an insulating layer 151. The
leave the pipe with a small but constant ambient ?eld,
electronic equipment of FIG. 21 may conveniently be
located in the housing ends :152 and 153. The sensing de
If the pipe is left with a stronger ?eld, more energy will
vice is supported for motion in the pipe 135 by wheeled
30 platforms 154 and 155. The flow of by-passed fluid
be required to reduce the net ambient ?eld to zero.
preferably in equilibrium with the earth’s magnetic ?eld.
Any magnetic discontinuity in the pipe, such as will be
caused by ?aws in the pipe, corrosion, welds, collars, sup
through apertures in the platform and around the outside
porting iron, etc. will result in a local concentration or
rarefaction ‘of the ambient ?eld. For example, if the
degausser is passed through the pipe so as to leave an
ambient ?eld from left to right or south to north, a thin
tral passage 156 may be provided to permit additional
fluid by-pass. Velocity of the sensing device in the pipe
may be controlled by automatically controlling the
amount of by-passed ?uid.
place in the pipe wall will result in a south seeking pole
at the left and a north seeking pole at the right. The
As mentioned previously, the principles of the in
vention are applicable not only to the logging of pipes
of the housing is shown by arrows.
In addition, a cen
presence of such a magnetic anomaly in the magnetic cir
but also to the inspection of other magnetic metal struc
cuit between the pole faces will, in effect, create a local 40 tures, such as tanks, beams and the like. An apparatus
net ambient ?eld which cannot be balanced out at the
for performing such inspection of an extensive metal sur
previously existing setting ‘of the slider of potentiometer
face is illustrated in FIGS. 23 and 24. In FIG. 23 the
142. However, presence of the net ambient ?eld will
iron surface ‘1611 might be the outside of a large steel tank
cause an ampli?ed 2]‘ signal to be delivered to the motor
or a large steel beam. The sensing element 161, which
140‘ which will cause the slider of potentiometer 142 to 45 may be, for example, of the type shown in FIG. 21, or
move toward a new null position. As a result, the cur
any of the others depicted, is disposed opposite the sur
rent ?owing through the coil ‘134 will be changed. This
face 1‘611‘. In order to isolate the surface segment oppo
change in current produces a voltage change across a re
site the detector from extraneous magnetic in?uences and
sistor 143’ which may be used as a measure of the
in ‘order to provide this segment with a standardized mag
strength of the net ambient ?eld produced by the anomaly. 50 netic history which will be the same as the history of all
The voltage across the resistor 143’ may be considered a
bias voltage since the ?ux in the coil 134» is a bias ?ux
intended to reduce the net DC. ?eld between the pole
faces to zero. The voltage change across the resistor
other segments traversed, there is provided an isolating
coil 162. The coil 162 is carried between annular legs
1163 and 164- of a magnetic structure 165. The legs 163
and 164 are joined magnetically by a core element 166
143' may be applied to an oscillator modulator 144’ to 55 which is remote from and generally parallel to the sur
modulate a suitable carrier, the modulated carrier being
face 161). The detecting element 161 is carried in the
recorded on a suitable device such as a wire recorder 145.
space within the leg 164. The legs 163‘ and 164 may be
The change in bias voltage, and hence the recorded quan
provided with wheels or casters 167’ to facilitate moving
tity, varies linearly with the change in magnetic character
the structure 165 over the surface 161). The gap pro
istics of the pipe which produces the change in bias volt 60 vided thereby also aids preventing the structure 165 from
age. The recorded information may subsequently be de
adhering ?rmly to the surface 160‘.
modulated in a linear demodulator and the demodulated
The coil 162 carries a current Which produces a satura
signal applied to a graphic recorder, as in FIG. 15.
tion ?ux in the iron disposed opposite the coil, in effect
In order for the recorded information to be meaningful,
completely magnetically isolating the iron segment oppo
it is necessary to know where along the pipe the anomaly 65 site the detector 161. As the structure 165 is caused to
occurred. This information may be provided as de
traverse the surface 160, the detector 161 comes oppo
scribed in connection with FIG. 16. Another means for
site an iron segment which had just previously been oppo
securing such positional information is shown in F1G. 21.
In this ?gure, a wheel 146 is arranged to be in contact
with the inside surface of the pipe and to rotate from
frictional engagement as the sensing device progresses.
Each time a predetermined number of revolutions has oc
curred, as determined by a suitable Geneva movement or
site the coil 162. Any magnetic anomalies in the segment
opposite the detector 161 will be sensed and recorded as
previously described.
Return of the iron from its saturated condition (when
opposite coil 162) to the equilibrium condition desired
for sensing is a transient effect which is limited in speed
by eddy currents. The speed of motion of the structure
the like, a switching mechanism :147 may be operated to
modulate the carrier frequency of an oscillator-modula 75 165 should not be so great that the radial distance be
tween the inner edge of the saturating coil 162 and the
slot extending around the periphery thereof at an inter
outer edge of the detecting or sensing zone will be tra
versed in a time interval in which eddy currents maintain
the ?ux in the detecting zone above its equilibrium value
as determined by the hyteresis loop of the iron. The
mediate point thereon, a generally U-shaped lining in said
slot, said lining being made from a magnetic material,
a pair of axially spaced, insulated coils wound around
said member within said slot, a third coil wound around
said member and disposed between the ?rst and second
coils, a saturable magnetic tape Wound around the turns
of said third coil in a direction generally radial with
thereto. For one quarter inch iron, a time of traverse
respect to said member, pipe engaging means attached
of this radial distance of about 0.1 second will generally
be satisfactory, while for one half inch iron the time may 10 to said supporting member adjacent each end thereof for
guiding the latter through said pipe under the force ex
be about 0.2 second.
erted thereon by the ?uid ?owing in said pipe.
The isolation coil 162 is preferably provided with a
5. Apparatus as set forth in claim 4 in which said pipe
DC. current component for saturating the iron opposite
permissible maximum speed of motion is thus related
to the thickness of the iron, being inversely proportional
engaging means includes a wheeled platform.
thereto and an AC. component to maintain the coil core
6. Apparatus as set forth in claim 4 in which said pipe
in equilibrium so that no ambient ?ux will disturb the 15
engaging means includes a deformable annular ?ange
detector. The saturation ?ux should, for most purposes,
having a diameter slightly greater than the internal diame
be of the order of 19,000 lines/cm.2 for the grades of
ter of said pipe.
iron generally used in tanks and similar structures. How
7. In apparatus for testing magnetic pipe, the combi
ever, lower ?uxes may be used Where the ?aws to be
detected are relatively large so that lower sensitivity de 20 nation comprising an annular supporting member made
of non-magnetic material and having a generally U-shaped
tection can be used, requiring less complete isolation.
slot extending around the periphery thereof, pipe engag
Where the core 166 is spaced relatively close to the
ing means for guiding said supporting member through
surface 160, the core 165 may be placed in magnetic
said pipe under the action of the ?uid carried by said
equilibrium by passing an alternating current through
a coil 167 which passes through holes 168 and 169‘ in 25 pipe, a generally U-shaped lining in said slot, said lining
being made vfrom :a magnetically soft iron, a pair of
the core 166. The core 166 and the legs 163 and 164
axially spaced, insulated coils wound around said member
are preferably made from an iron With a low coercive
within said slot, a third coil wound around said mem
force to facilitate degaussing 0f the core and legs.
The pole faces of the detector can be shaped to ac—
ber and disposed between the ?rst and second coils, a tape
commodate the character of the surface being inspected. 30 wound around the terms of said third coil in a direc
The shape of the structure 165 can similarly be selected
tion generally radial with respect to said member, said
tape being readily saturable at a predetermined frequency,
to accommodate particular surface con?gurations.
a source of sinusoidal alternating current of said fre
quency, means to connect said source to said third coil,
illustrated in FIG. 23 may be used for this purpose, as 35 a pass ?lter tuned to the second harmonic of said fre
In some cases it may be desirable magnetically to iso
late a section of pipe. The magnetic isolation principle
shown in FIG. 26. In FIG. 26, a north seeking radial
magnet 175 and a south seeking radial magnet 176 joined
quency and connected to said ?rst and second coils, and
a recording mechanism coupled to the output of said
by an iron core 177 precede the detector or sensing struc
?lter for recording, as a function of time, impulses of
ture 178, while a north seeking radial magnet 1'79 and a
energy at said second harmonic frequency induced in
south seeking radial magnet 180‘ joined by an iron core 40 said ?rst and second coils.
181 follow the sensing structure. The magnet assemblies
8. Apparatus as set forth in claim 7 in which said
and the sensing structure may be separated by a ?exible
source, said ?lter and said recording mechanism are car
non-magnetic member 183, which might be a rubber hose.
ried by said supporting member.
The magnets should create suf?cient ?ux to saturate the
9. In apparatus for testing magnetic pipe, the combi
adjacent iron in the pipe 182, thereby achieving both a 45 nation comprising a supporting member made of non
standardized magnetic history and magnetic isolation of
the sensing structure. The north and south seeking poles
can, of course, be interchanged.
While the invention has been described in connection
magnetic material and having a generally U-shaped slot
extending around at least a portion of the periphery
thereof, said supporting member being constructed so as
to pass through said pipe in an axial direction, a generally
with speci?c embodiments thereof and in speci?c uses, 50 U-shaped lining in said slot, said lining being made from
various modi?cations thereof will occur to those skilled
a magnetic material, a pair of axially spaced, insulated
in the art without departing from the spirit and scope
coils wound around said member within said slot, a third
of the invention as set forth in the appended claims.
coil wound around said member and disposed between
What is claimed is:
the ?rst and second coils, and a saturable magnetic tape
1. In apparatus for testing magnetic pipe, the combina
wound around the turns of said third coil in a direction
tion comprising a generally circular supporting member
generally radial with respect to said member and for a
made of non-magnetic material and having a generally
predetermined arc of the periphery of said member.
U-shaped slot extending around the periphery thereof, a
10. In apparatus for testing magnetic pipe, the com
generally U-shaped lining in said slot, said lining being
bination comprising an annular supporting member made
made from a magnetic material, a pair of axially spaced, 60 of non-magnetic material and having a generally U-shaped
insulated coils wound around said member Within said
slot extending around the periphery thereof, a generally
slot, a third coil wound around said member and disposed
U-shaped lining in said slot, said lining being made from
between the ?rst and second coils, and a saturable mag
a magnetic material, a pair of axially spaced, insulated
netic tape wound around the turns of said third coil in a
coils wound around said member within said slot, a
direction generally radial with respect to said member. 65 third coil wound around said member and disposed be
2. Apparatus as set forth in claim 1 in which said gen
tween the ?rst and second coils, and a saturable magnetic
erally U-shaped lining is constructed so that the ends
tape Wound around the turns of said third coil in a direc
thereof approach closely the Walls of said pipe when said
tion generally radial with respect to said member and
apparatus is inserted therein.
for a limited arc of the periphery of said member.
3. Apparatus as set forth in claim 1 in which said tape 70
11. Apparatus as set forth in claim- 10 in which said
is made of relatively thin steel which is readily saturable
tape is wound around the turns of said third coil over
at a frequency of the order of 750 cycles per second.
a plurality of spaced arcs of the periphery of said mem
4. In apparatus for testing magnetic pipe, the combi
nation comprising an annular supporting member made
of non-magnetic material and having a generally U-shaped 75
(References on following page)
References Cited in the ?le of this patent
' Minor et al. __________ __ Oct. 13, 1953
Falk ______________ __ Nov. 15, 1949
Cole ________________ __ July 15, 1952
2,834,1 13
Lloyd ______________ __ Aug. 25, 1953
De Witte _______ __. ____ __ July 11, 1961
Sperry ______________ __ July 19, 1932
Dana ________________ __ Dec. 18, 1934
Frickey et a1. ________ __ Nov. 13, 1945
Barnes et a1 ___________ __ Mar. 2, 1954
Dionne ______________ __ Mar. 27, 1956
Cooley ______________ __ Nov. 13, 1956
Stateman et a1. ______ __ Dec. 17, 1957
En Dean et a1 _________ __ May 13, 1958
Ball et ‘a1, ____________ __ July 1, 1958
Nettles et a1. ________ __ June 23, 1959
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